Re: STL set lower_bound

From:
mattg <gara.matt@gmail.com>
Newsgroups:
comp.lang.c++
Date:
Sun, 29 Mar 2009 15:20:09 -0700 (PDT)
Message-ID:
<6bf53876-aa20-4cff-b622-ce6beb0ec286@n7g2000prc.googlegroups.com>
On Mar 29, 2:39 pm, Paavo Helde <pa...@nospam.please.ee> wrote:

mattg <gara.m...@gmail.com> kirjutas:

On Mar 29, 2:24 pm, Paavo Helde <pa...@nospam.please.ee> wrote:

mattg <gara.m...@gmail.com> kirjutas:
[...]

void test(){
     s1.insert((new node(1)));
     s1.insert((new node(2)));
     s1.insert(new node(8));
     s1.insert(new node(9));
     s1.insert(new node(12));

[...]

     iter = s1.lower_bound(new node(5));

outputs

iter = 8

instead of

iter = 2

?


Because that's how lower_bound is defined:

"Returns an iterator to the first element in a set with a key that is
equ

al

to or greater than a specified key"

If you want the previous element, you can check the result against
s1.beg

in

() and decrement the iterator.

hth
Paavo


so something like:

if(iter != s1.begin())
{
   node* lessthan = *(--iter); //this is the node less than the q=

uery

}


Yes, something like that. And I hope you are realizing you are leaking
memory all over the place, and the design would become much simpler by
using std::set<node>.

BEst regards
Paavo


yes I realize I am leaking memory everywhere, this was simply a test,
in my actual application I clean up. My original attempt at this was
using node as a struct instead of a class but I couldn't figure out
how to write the line

iter = s1.lower_bound(new node(5));

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